Copper wire and method of manufacturing the same

ABSTRACT

A copper wire includes a copper wire rod including 5 to 55 mass ppm of Ti, 3 to 12 mass ppm of sulfur, and 2 to 30 mass ppm of oxygen with the balance copper and inevitable impurities, a first crystal including a [111] crystal orientation and at least one twin crystal therein, and a second crystal that includes one or more crystals adjacent to the first crystal, a [111] crystal orientation with a different rotation angle on an atomic plane from the first crystal, and at least one twin crystal therein.

The present application is based on Japanese patent application No. 2013-078927 filed on Apr. 4, 2013, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a copper wire and a method of manufacturing the copper wire.

2. Description of the Related Art

G. Bassi: Trans. AIME, Journal of Metals, July (1952) 753-754 (hereinafter NPL-1) reports that a tough pitch copper (3N copper) wire containing 0.04% of oxygen is initially provided with a [111] crystal orientation before wire drawing, then drawn at a compression ratio of 90.0 to 99.7% and annealed at 400° C. for 2 hours so as to have a [100] crystal orientation, and high temperature annealing at 950° C. for 1 hour followed by a secondary recrystallization is then conducted so as to have a fiber structure with a [111] crystal orientation. NPL-1 also reports that it is initially provided with a [100] crystal orientation before the wire drawing process, then drawn at a compression ratio of 90.0 to 99.7% and annealed at 400° C. for 2 hours so as to have a mixture of [100] and [112] crystal orientations, and high temperature annealing at 950° C. for 1 hour is then conducted so as to have a mixture of [100], [112] and [111] crystal orientations.

JP-B-H07-118216 discloses an audio/image device conductor formed of Cu of 99.999 wt % as a face-centered cubic lattice crystal, a single crystal or a crystal aggregate such that a longitudinal orientation is within 10 degrees from the [111] or [100] crystal orientation in order to improve sound and image quality of audio/image devices.

JP-B-4914153 discloses an audio/video signal conductor formed of a metal wire-like material and configured so that the relation of I(111)≧I(200) is satisfied when an x-ray is irradiated on a cross section of a copper wire, where I(111) is x-ray diffraction intensity of the (111) plane and I(200) is x-ray diffraction intensity of the (200) plane.

Takeshi Takubo and Teruichi Honda, Copper and Copper alloy, Vol. 46, No. 1 (2007) 17-20 (hereinafter NPL-2) which is related to JP-B-4914153, reports that, when copper wires with different purities which have been primarily recrystallized are further annealed, crystal grain coarsening, an increase in the [111] axis density and a decrease in the [100] axis density occur in high purity copper (6N copper) but such a phenomenon does not occur in oxygen-free copper (4N copper).

JP-A-2010-205623 discloses that a value of I₍₂₀₀₎/I_(O(200)) is not more than 3 where I₍₂₀₀₎ is a ratio of x-ray diffraction intensity on the (200) plane to that on the (111) plane which are derived by x-ray diffraction performed on a surface of a winding conductor having an insulating film thereon and I_(O(200)) is a ratio of x-ray diffraction intensity on the (200) plane to that on the (111) plane measured on fine powder copper.

JP-A-S60-203339 discloses that a casting material obtained by a heated mold continuous casting process or a casting material formed of a single crystal is processed to manufacture a wire for audio device. JP-A-S60-203339 also discloses that distortion, which is dislocation, remains when a material in the form of single crystal is processes and it is thus necessary to use copper without distortion.

SUMMARY OF THE INVENTION

The tough pitch copper wire reported in NPL-1 has a problem that a half-softening temperature is relatively high even though tensile strength is high. In addition, the tough pitch copper wire also has a problem that weld-ability thereof is inferior to that of oxygen-free copper, etc., because vapor is generated by combination of oxygen inside the tough pitch copper with hydrogen at the time of welding and causes cracks to occur at the welded portion.

The copper wires formed of high purity copper and copper with higher purity than the high purity copper which are reported in NPL-2 have a low half-softening temperature but crystals in these copper wires are coarsened due to secondary recrystallization when heat-treated, and there is thus a tendency that tensile strength of the copper wire is low. In addition, there is also a problem that these copper wires are expensive.

In the method of manufacturing a copper wire disclosed in JP-B-4914153, copper constituting the copper wire is high purity copper with purity of not less than 99.9999% and it is possible to manufacture a copper wire in which a ratio of x-ray diffraction intensity on the (111) plane to that on the (200) plane measured on the cross section of the copper wire is 21.4:1. However, this method has a problem that it is necessary to use high purity copper to manufacture copper wires.

Furthermore, although JP-B-H07-118216 describes a method of manufacturing a copper wire in which a longitudinal orientation of the copper wire is within 10° from the [111] or [100] crystal orientation, this method of manufacturing a copper wire is expensive and thus has a problem that it is not possible to mass-produce copper wires.

It is an object of the invention to provide a copper wire that satisfies a lower half-softening temperature than tough pitch copper (3N copper) and oxygen-free copper (4N copper) and higher tensile strength than high purity copper (6N copper), as well as a method of manufacturing the copper wire.

(1) According to one embodiment of the invention, a copper wire comprises:

a copper wire rod comprising 5 to 55 mass ppm of Ti, 3 to 12 mass ppm of sulfur, and 2 to 30 mass ppm of oxygen with the balance copper and inevitable impurities;

a first crystal comprising a [111] crystal orientation and at least one twin crystal therein; and

a second crystal that comprises one or more crystals adjacent to the first crystal, a [111] crystal orientation with a different rotation angle on an atomic plane from the first crystal, and at least one twin crystal therein.

In the above embodiment (1) of the invention, the following modifications and changes can be made.

(i) The first or second crystal is not more than 100 μm in size.

(ii) The twin crystal in the first or second crystal is formed at a distance of not less than 0.1 mm and not more than 0.5 mm.

(iii) The copper wire further comprises a half-softening temperature of not less than 130° C. and not more than 200° C.

(iv) The copper wire further comprises a thin film that comprises Sn, Ag, solder, amorphous zinc and oxygen and is formed on a surface of the copper wire rod.

(2) According to another embodiment of the invention, a method of manufacturing a copper wire comprises conducting a heat treatment to a copper wire rod comprising 5 to 55 mass ppm of Ti, 3 to 12 mass ppm of sulfur, and 2 to 30 mass ppm of oxygen with the balance copper and inevitable impurities under a condition of a heat treatment temperature of not less than 700° C. and not more than 950° C. and heat treatment time of not less than 60 minutes and not more than 120 minutes so as to obtain a copper wire comprising a first crystal comprising a [111] crystal orientation and at least one twin crystal therein and a second crystal that comprises one or more crystals adjacent to the first crystal, a [111] crystal orientation with a different rotation angle on an atomic plane from the first crystal and at least one twin crystal therein.

In the above embodiment (2) of the invention, the following modifications and changes can be made.

(v) The heat treatment is conducted in an argon or nitrogen atmosphere by using a tubular electric furnace, an electric annealer, a gold furnace or continuous plasma heat treatment.

Effects of the Invention

According to one embodiment of the invention, a copper wire can be provided that satisfies a lower half-softening temperature than tough pitch copper (3N copper) and oxygen-free copper (4N copper) and higher tensile strength than high purity copper (6N copper), as well as a method of manufacturing the copper wire.

BRIEF DESCRIPTION OF THE DRAWINGS

Next, the present invention will be explained in more detail in conjunction with appended drawings, wherein:

FIG. 1 is a photograph showing a cross-sectional structure of Example 1 of the present invention;

FIG. 2 is a photograph showing a cross-sectional structure of Comparative Example 1;

FIG. 3 is a photograph showing a cross-sectional structure of Comparative Example 2;

FIG. 4 is a photograph showing a cross-sectional structure of Comparative Example 3;

FIG. 5 is a diagram illustrating x-ray diffraction intensity obtained from the cross-sectional structure of Example 1 of the invention;

FIG. 6 is a diagram illustrating x-ray diffraction intensity obtained from the cross-sectional structure of Comparative Example 1;

FIG. 7 is a diagram illustrating x-ray diffraction intensity obtained from the cross-sectional structure of Comparative Example 2; and

FIG. 8 is a diagram illustrating x-ray diffraction intensity obtained from the cross-sectional structure of Comparative Example 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Summary of the Embodiment

A copper wire in the present embodiment is formed of a copper wire rod containing Ti at a concentration of 5 to 55 mass ppm, sulfur at a concentration of 3 to 12 mass ppm, oxygen at a concentration of 2 to 30 mass ppm and the balance consisting of copper and inevitable impurities, and the copper wire includes a first crystal having a [111] crystal orientation and including at least one twin crystal therein and a second crystal which is one or more crystals adjacent to the first crystal, has a [111] crystal orientation provided by rotating the atomic plane at a different angle from the first crystal and includes at least one twin crystal therein.

Embodiment

The copper wire in the present embodiment is formed of a copper wire rod containing Ti at a concentration of 5 to 55 mass ppm, sulfur at a concentration of 3 to 12 mass ppm, oxygen at a concentration of 2 to 30 mass ppm and the balance consisting of copper and inevitable impurities. Note that, the inevitable impurity means a substance inevitably mixed during the production process.

The copper wire has a first crystal and a second crystal. The first crystal has a crystal orientation and includes at least one twin crystal therein. The second crystal is one or more crystals adjacent to the first crystal, has a [111] crystal orientation provided by rotating the atomic plane at a different angle from the first crystal and includes at least one twin crystal therein. The first or second crystal is not more than 100 μm in size and the twin crystals therein are formed at a distance of not less than 0.1 mm and not more than 0.5 mm.

The copper wire has a conductivity of not less than 101% IACS (International Annealed Copper Standard, conductivity is defined as 100% at 1.7241×10⁻⁸ Ωm), half-softening temperature of not less than 130° C. and not more than 200° C., tensile strength of not less than 200 MPa and an elongation percentage of not less than 25%.

NPL-2 has reported that a percentage of planes in the [111] crystal orientation in high purity copper (6N copper) is increased by further heat treatment after primary recrystallization but such a phenomenon is not observed in oxygen-free copper (4N copper). In addition, a mixture of [111] and [100] crystal orientations is also observed in the high purity copper. It should be noted that NPL-2 does not mention an increase in a percentage of planes in the [111] crystal orientation in a copper wire rod which contains Ti, etc.

The present inventors found that it is possible to manufacture a copper wire in which a percentage of planes in the [111] crystal orientation is substantially 100% when a copper wire rod containing Ti at a concentration of 5 to 55 mass ppm, sulfur at a concentration of 3 to 12 mass ppm and oxygen at a concentration of 2 to 30 mass ppm is heated within a temperature range causing secondary recrystallization (700 to 950° C.).

Composition of Copper Wire Rod

The sulfur concentration in the copper wire rod is desirably lower. However, since general electrolytic copper to be a raw material of the copper wire rod is manufactured by electric purification in a cupric sulfate solution, incorporation of sulfur into the copper wire rod is unavoidable and it is thus difficult to adjust the sulfur concentration to not more than 3 mass ppm. On the other hand, the upper limit of the sulfur concentration in the copper wire rod in general electrolytic copper is set to be 12 mass ppm. Therefore, the sulfur concentration in the copper wire rod is in a range of 3 to 12 mass ppm.

The oxygen concentration in the copper wire rod is set to not less than 2 mass ppm since the softening temperature thereof is not lowered when the oxygen concentration is low. On the other hand, if the oxygen concentration is more than 30 mass ppm, then steam generated by combination of oxygen with hydrogen during solidification of molten copper causes a blowhole and this may cause flaws to be generated on the surface of the copper wire rod. Therefore, the oxygen concentration in the copper wire rod is in a range of 2 to 30 mass ppm.

When the Ti concentration in the copper material is low, sulfur which is an inevitable impurity present in the copper material cannot be sufficiently trapped and precipitated. Therefore, the Ti concentration is set to be not less than 5 mass ppm. On the other hand, if the Ti concentration is more than 55 mass ppm, excessive Ti is solid-dissolved in copper and this causes a decrease in conductivity or an increase in softening temperature. Therefore, the Ti concentration is set to be not more than 55 mass ppm.

Dispersed Particles in Copper Wire

Dispersed particles in the copper wire serve as a precipitation site of sulfur which is contained in the copper wire rod. Therefore, the dispersed particles are preferably small in size and distributed in a large amount. Sulfur and oxygen in the copper wire rod and Ti to be added to the copper wire rod are aggregated into a compound of TiO, TiO₂, TiS or TiOS, thereby forming the dispersed particles.

Preferably, the size of the dispersed particles is not more than 200 nm for TiO, not more than 1000 nm for TiO₂, not more than 200 nm for TiS and not more than 300 nm for TiOS so as to serve as a precipitation site of sulfur. The size of the dispersed particle to be formed varies depending on the manufacturing conditions of molten copper during casting of copper wire. Therefore, it is also necessary to optimize the manufacturing conditions of copper wire.

Method of Manufacturing Copper Wire

Following is an example of a method of manufacturing a copper wire in the present embodiment. The case of manufacturing an 8 mm diameter-copper wire from a copper wire rod by SCR (South Continuous Rod System) continuous casting and rolling will be described as an example.

Copper to be a material of the copper wire is melted in a shaft furnace and, after adding Ti to molten copper, a copper wire rod is casted at a casting temperature of not less than 1100° C. and not more than 1320° C. under reductive gas (CO) atmosphere while controlling concentrations of sulfur and oxygen.

When the temperature of the copper wire rod in a molten state is high, blowholes are formed and cause deterioration in the surface quality of the copper wire and also the particle size of the dispersed particles tends to be large. Therefore, the casting temperature is not more than 1320° C. On the other hand, at the temperature of less than 1100° C., the copper wire rod in a molten state is likely to solidify and the manufacturing of the copper wire is not stable. Therefore, the casting temperature is not less than 1100° C. and not more than 1320° C.

Next, the casting product obtained by the SCR continuous casting and rolling is hot-rolled to manufacture an 8 mm-diameter copper wire rod (a compression ratio of 99.3%).

The hot-rolling temperature is not less than 550° C. and not more than 880° C. which is lower than the typical hot-rolling temperature (not less than 900° C. and not more than 950° C.) in order to decrease a solid solubility limit of sulfur so that sulfur is precipitated during the hot rolling. The hot-rolling temperature of less than 550° C. causes an increase in flaws on the copper wire, and hence, the hot-rolling temperature is set to not less than 550° C. Meanwhile, the hot-rolling temperature is desirably as low as possible and is thus set to not more than 880° C.

Next, the copper wire rod is subjected to heat treatment as follows. The copper wire rod is heat-treated using a tubular electric furnace under the conditions of a heat treatment temperature of not less than 700° C. and not more than 950° C., which is in a heating temperature range causing secondary recrystallization, and heat treatment time of not less than 60 minutes and not more than 120 minutes in an inert gas (nitrogen) atmosphere. A copper wire, in which substantially 100% of plane is the (111) plane perpendicular to the [111] crystal orientation, is thereby obtained. Alternatively, the copper wire rod may be heat-treated in an argon or nitrogen atmosphere by an electric annealer, a gold furnace or continuous plasma heat treatment.

Effects of the Embodiment

The present embodiment achieves the following effects.

(1) Heat treatment on the copper wire rod containing Ti, sulfur and oxygen provides a copper wire in which a percentage of planes in the [111] crystal orientation is substantially 100% while having a twin structure, which allows the copper wire formed of the copper wire rod to have tensile strength higher than a copper wire formed of high purity copper (6N copper) and equivalent to copper wires formed of tough pitch copper (3N copper) and oxygen-free copper (4N copper).

(2) Since the copper wire rod is formed so that a percentage of planes in the [111] crystal orientation is substantially 100% and the size of crystal constituting the copper wire is increased, a microscopic capacitor effect caused by the crystal in the copper wire can be reduced. As a result, it is possible to reduce distortion of signals transmitted through the copper wire.

(3) Adding Ti at a concentration of 5 to 55 mass ppm to the copper wire rod and adjusting the oxygen concentration in the copper wire rod to 2 to 30 mass ppm allow the copper wire to have a half-softening temperature lower than the copper wires formed of tough pitch copper (3N copper) and oxygen-free copper (4N copper) and equivalent to the copper wire formed of high purity copper (6N copper).

(4) It is possible to manufacture a copper wire having high tensile strength without requiring complicated heat treatment processes.

EXAMPLE

Next, Example of the invention will be described in reference to FIGS. 1 to 8.

FIG. 1 is a photograph showing a cross-sectional structure of Example 1 of the invention.

FIG. 2 is a photograph showing a cross-sectional structure of Comparative Example 1.

FIG. 3 is a photograph showing a cross-sectional structure of Comparative Example 2.

FIG. 4 is a photograph showing a cross-sectional structure of Comparative Example 3.

FIG. 5 is a diagram illustrating x-ray diffraction intensity obtained from the cross-sectional structure of Example 1 of the invention. FIG. 6 is a diagram illustrating x-ray diffraction intensity obtained from the cross-sectional structure of Comparative Example 1. FIG. 7 is a diagram illustrating x-ray diffraction intensity obtained from the cross-sectional structure of Comparative Example 2. FIG. 8 is a diagram illustrating x-ray diffraction intensity obtained from the cross-sectional structure of Comparative Example 3.

Here, Example 1 is a copper wire formed of a copper wire rod with the oxygen concentration of 7 to 8 mass ppm, a sulfur concentration of 5 mass ppm and a Ti concentration of 13 mass ppm, Comparative Example 1 is a copper wire formed of tough pitch copper (3N copper), Comparative Example 2 is a copper wire formed of oxygen-free copper (4N copper) and Comparative Example 3 is a copper wire formed of high purity copper (6N copper).

Each of the copper wires in Example 1 and Comparative Examples 1 to 3 was made by cold-drawing a copper wire rod from 8 mm to 2.6 mm in diameter (a compression ratio of 90%). On each copper wire, a cross section was observed and concentrations of oxygen, sulfur and Ti, a half-softening temperature, conductivity, tensile strength, an elongation percentage and x-ray diffraction intensity were measured.

The copper wire was cut to 70 cm and used to measure conductivity of the copper wire. That is, using a four-terminal method in which a distance between current terminals was set to 60 cm and a distance between voltage terminals was set to 50 cm, a current of 4 A was fed to each copper wire and the conductivity was measured at room temperature.

A half-softening temperature of the copper wire was measured as follow. That is, tensile strength at room temperature and tensile strength after heat treatment at a temperature of 100 to 400° C. for 60 minutes were measured on each copper wire. Then, a heat treatment temperature corresponding to a tensile strength midway between the tensile strength at room temperature and tensile strength after heat treatment was derived, and the derived heat treatment temperature was defined as a half-softening temperature.

Concentrations of oxygen, sulfur and Ti in the copper wire were measured by an infrared emission analyzer (Leco: registered trademark).

Tensile strength was measured using a precision universal tester: Autograph AG-100KNG (manufactured by Shimadzu Corporation). Each copper wire was cut to 35 cm and tensile strength thereof was measured under the conditions of a measurement distance of 25 cm and a tension rate of 20 mm/min.

Using the autograph precision universal tester mentioned above, a difference between a length of the joined copper wire after breakage and the original length of the copper wire was divided by the original length of the copper wire, the elongation percentage was derived from the obtained value.

X-ray diffraction intensity of the copper wire was measured using an X-ray measuring device: RINT 2000 (manufactured by Rigaku Corporation). That is, a 2.6 mm-diameter copper wire embedded in a resin was set on the X-ray measuring device so that an x-ray was irradiated on the cross section of the copper wire and x-ray diffraction intensity was measured at an angle from 0 to 90° by the θ-2θ method under the conditions that output of the x-ray tube of the X-ray measuring device was 40 kV, 150 mA and 3°/min.

A half-softening temperature, tensile strength, an elongation percentage and x-ray diffraction intensity were measured after each copper wire was heat-treated under the conditions of a heat treatment temperature of 900° C. and heat treatment time of 1 hour in an inert gas (nitrogen) atmosphere.

Example 1

As shown in FIG. 1, it can be confirmed that crystal grains 1 a and 1 b in the crystal structure of Example 1 are larger than crystal grains 1 in Comparative Examples 1 to 3 shown in FIGS. 2 to 4. It can be also confirmed that the formation direction of twin crystal is different between a twin crystal 2 a in the crystal grain 1 a and a twin crystal 2 b in the crystal grain 1 b and that a rotated angle of the atomic plane is different between the crystal grains 1 a and 1 b. It can be confirmed that a distance between twin crystals formed in the crystal structure is not less than 0.1 mm and not more than 0.5 mm.

In Example 1, an x-ray diffraction peak is observed only from the (111) plane and is not observed from any of the (200), (220) and (311) planes, as shown in FIG. 5. This confirms that a percentage of planes in the [111] crystal orientation is substantially 100% in the copper wire of Example 1.

Comparative Example 1

As shown in FIG. 2, it can be confirmed that the crystal grain 1 in Comparative Example 1 is smaller than the crystal grains 1 a and 1 b in Example 1 shown in FIG. 1 and the crystal grains 1 in Comparative Examples 2 and 3 shown in FIGS. 3 and 4. A twin crystal 2 is also observed in the crystal structure of Comparative Example 1. In Comparative Example 1, x-ray diffraction peaks are observed from the (111), (200), (220) and (311) planes, as shown in FIG. 6. This confirms that the [111], [200], [220] and [311] crystal orientations are mixed in the copper wire in Comparative Example 1.

Comparative Example 2

As shown in FIG. 3, it can be confirmed that the crystal grain 1 in Comparative Example 2 is larger than the crystal grain 1 in Comparative Example 1 shown in FIG. 2. The twin crystal 2 is also observed in the crystal structure of Comparative Example 2. In Comparative Example 2, an x-ray diffraction peak is observed only from the (111) plane and is not observed from any of the (200), (220) and (311) planes, as shown in FIG. 7. This confirms that a percentage of planes in the [111] crystal orientation is substantially 100% in the copper wire of Comparative Example 2.

Comparative Example 3

As shown in FIG. 4, it can be confirmed that the crystal grain 1 in the crustal structure of the Comparative Example 3 is coarsened and larger than the crystal grains 1 in Comparative Examples 1 and 2 shown in FIGS. 2 and 3. The twin crystal 2 is also observed in the crystal structure of Comparative Example 3. In Comparative Example 3, x-ray diffraction peaks are observed from the (111), (200) and (220) planes, as shown in FIG. 8. This confirms that the [111], [200] and [220] crystal orientations are mixed in the copper wire in Comparative Example 3.

Overall Evaluation of Example and Comparative Examples

Table 1 shows concentrations of oxygen, sulfur and Ti, a half-softening temperature, conductivity, tensile strength, an elongation percentage, x-ray diffraction intensity and overall evaluation of Example 1 and Comparative Examples 1 to 3.

In Example 1, the half-softening temperature is not more than 200° C., the tensile strength is not less than 200 MPa, the elongation percentage is not less than 20%, the conductivity is not less than 101% IACS and no x-ray diffraction peak but from the (111) plane is observed, hence, the overall evaluation was “◯ (good)”.

In Comparative Example 1, the half-softening temperature is not more than 200° C., the tensile strength is not less than 200 MPa, the elongation percentage is not less than 20% and the conductivity is not less than 101% IACS but x-ray diffraction peaks other than from the (111) plane are also observed, hence, the overall evaluation was “X (bad)”.

In Comparative Example 2, the tensile strength is not less than 200 MPa, the elongation percentage is not less than 20%, the conductivity is not less than 101% IACS and no x-ray diffraction peak but from the (111) plane is observed, however, the half-softening temperature is more than 200° C., hence, the overall evaluation was “X”. Furthermore, the elongation percentage in Comparative Example 2 is not less than 20% but is lower than that of the copper wire rod of the invention which is Example 1. This result shows that the copper wire rod of the invention has higher elongation than oxygen-free copper, etc., even after high temperature heat treatment.

In Comparative Example 3, the half-softening temperature is not more than 200° C. and the conductivity is not less than 101% IACS but the tensile strength is less than 200 MPa, the elongation percentage is less than 20% and x-ray diffraction peaks other than from the (111) plane are also observed, hence, the overall evaluation was “X”.

TABLE 1 Half- Oxygen Sulfur Ti softening Tensile X-ray Copper wire concentration concentration concentration temperature Conductivity strength Elongation diffraction Overall rod (mass ppm) (mass ppm) (mass ppm) (° C.) (% IACS) (MPa) (%) intensity evaluation Example 1 7 to 8 5 13 134 101.0 242 28 ◯ ◯ ◯ ◯ ◯ ◯ Comparative 300 5 — 190 101.0 243 32 X X Example 1 ◯ ◯ ◯ ◯ (tough pitch copper (3N copper)) Comparative not more 5 — 230 101.5 243 21 ◯ X Example 2 than 1 X ◯ ◯ ◯ (oxygen-free copper (4N copper)) Comparative — — — 130 102.8 186 19 X X Example 3 ◯ ◯ X X (high purity copper (6N copper)) Not more than 200° C. of half-softening temperature is evaluated as good (i.e. ◯). Not more than 200 MPa of tensile strength is evaluated as good (i.e. ◯). Not more than 101% of conductivity is evaluated as good (i.e. ◯). Not more than 20% of elongation percentage is evaluated as good (i.e. ◯).

Three copper wire rods, each of which is the same as the copper wire rod used in Example 1, were prepared and heat-treated under the conditions of respective heat treatment temperatures of 600° C., 700° C. and 950° C. and heat treatment time of 1 hour for each in an inert gas (nitrogen) atmosphere, and then, crystal orientation was checked on the respective copper wire rods which were heat-treated at different temperatures. As a result, a percentage of planes in the [111] crystal orientation was substantially 100% in the copper wire rods heat-treated at temperatures of 700° C. and 950° C. On the other hand, in the copper wire rod heat-treated at a temperature of 600° C., a percentage of planes in the [111] crystal orientation was not substantially 100% and crystal orientations of [200], [230] and were also present. That is, by heat-treating a copper wire rod having a predetermined composition at a heat treatment temperature of 700 to 950° C., it is possible to obtain a copper wire rod in which a percentage of planes in the [111] crystal orientation is substantially 100%. In addition, such a copper wire rod has better tensile strength and elongation than high-quality high purity copper (6N copper) and has an advantage that breakage is less likely to occur even when being bent.

Modifications

The embodiment and Example of the invention are not intended to be limited to the above-mentioned embodiment and Example, and the various kinds of modifications can be implemented without changing the gist of the invention. For example, the copper wire in Example may be a single wire formed by covering a copper wire with an insulation or a wire assembly formed of plural single wires.

In addition, it may be embodied as a twisted wire formed by twisting plural copper wires each formed by covering a copper wire rod with an insulation.

In addition, two or more selected from heat-treated tough pitch copper, oxygen-free copper and high purity copper may be used for a copper wire of the wire assembly or of the twisted wire.

In addition, it may be embodied as a power cable or signal cable formed by providing an insulation layer on the outer periphery of a copper wire formed using the copper wire rod or a twisted wire formed using the copper wire rod. In addition, it may be embodied as a coaxial cable formed by providing an insulation layer and a braided wire on the outer periphery of a center conductor formed of the copper wire rod.

In addition, although the copper wire rod manufactured by a SCR continuous casting and rolling machine has been described in the embodiment, the copper wire rod may be manufactured by an apparatus integrally performing casting and rolling, such as twin-roll continuous casting and rolling apparatus or Properzi continuous casting and rolling machine.

In addition, the copper wire may be configured such that a thin film containing Sn, Ag, solder, amorphous zinc and oxygen is formed on a surface of the copper wire rod.

INDUSTRIAL APPLICABILITY

The invention is applicable to, e.g., wirings or enamel wires used in motor, etc., conductors for audio cables of earphones or headphones, etc., and signal conductors for car navigation systems, etc., required to provide high sound and image quality. 

What is claimed is:
 1. A copper wire, comprising: a copper wire rod comprising 5 to 55 mass ppm of Ti, 3 to 12 mass ppm of sulfur, and 2 to 30 mass ppm of oxygen with the balance copper and inevitable impurities; a first crystal comprising a [111] crystal orientation and at least one twin crystal therein; and a second crystal that comprises one or more crystals adjacent to the first crystal, a [111] crystal orientation with a different rotation angle on an atomic plane from the first crystal, and at least one twin crystal therein.
 2. The copper wire according to claim 1, wherein the first or second crystal is not more than 100 μm in size.
 3. The copper wire according to claim 1, wherein the twin crystals in the first or second crystal are formed at a distance of not less than 0.1 mm and not more than 0.5 mm.
 4. The copper wire according to claim 1 further comprising a half-softening temperature of not less than 130° C. and not more than 200° C.
 5. The copper wire according to claim 1 further comprising a thin film that comprises Sn, Ag, solder, amorphous zinc and oxygen and is formed on a surface of the copper wire rod.
 6. A method of manufacturing a copper wire, comprising conducting a heat treatment to a copper wire rod comprising 5 to 55 mass ppm of Ti, 3 to 12 mass ppm of sulfur, and 2 to 30 mass ppm of oxygen with the balance copper and inevitable impurities under a condition of a heat treatment temperature of not less than 700° C. and not more than 950° C. and heat treatment time of not less than 60 minutes and not more than 120 minutes so as to obtain a copper wire comprising a first crystal comprising a [111] crystal orientation and at least one twin crystal therein and a second crystal that comprises one or more crystals adjacent to the first crystal, a [111] crystal orientation with a different rotation angle on an atomic plane from the first crystal and at least one twin crystal therein.
 7. The method according to claim 6, wherein the heat treatment is conducted in an argon or nitrogen atmosphere by using a tubular electric furnace, an electric annealer, a gold furnace or continuous plasma heat treatment. 